Heart Care

Winter Months Bring Elevated Blood Pressure, Experts Say

It turns out blood pressure has a chill factor: Hypertension is harder to control in colder weather, according to experts at a recent meeting of the American Heart Association.

This concept has been around a while says a heart expert.

"It has been noted for decades that people's blood pressure tends to be a little bit harder to control or a little bit higher in cold climates," says Dr. Kenneth Baker, at the Texas A&M Health Science Center in Temple, Texas.

Cold = Vasoconstriction = Hypertension

The study was led by Dr. Ross Fletcher of Georgetown University. The researchers drew on a vast database: the Veterans Administration's storehouse of 1.8 billion vital statistics records.

The five-year study looked at electronic health records for almost 1.2 million patients cared for at 15 VA hospitals located at different latitudes: Anchorage; Baltimore; Boston; Chicago; Fargo, ND; Honolulu; Houston; West Los Angeles; Miami; Minneapolis; New York City; Philadelphia; San Juan, Puerto Rico; Portland, Oregon; and Washington, DC.

The average age of participants was 66. Fifty-one percent were Caucasian, 21 percent were Hispanic, and 27 percent were African American. Less than 4 percent were female.

Within the sample, almost 444,000 veterans had high blood pressure (based on readings of more than 140/90 on three separate days).

And, regardless of their locale, patients experienced an average difference of almost 8 percent in getting their high blood pressure back to normal between winter and summer, with that feat being much tougher in winter.

Outside expert Dr. Baker speculated about any number of reasons.

"My guess is that one of the top reasons is, when you're in a cold atmosphere, you vasoconstrict [blood vessels narrow]," he says.

"If you stick your hand in ice water, it has the same effect," notes Dr. Baker. "Blood pressure goes up a little, and in hotter climates, sitting by the pool in your swimming suit, the vessels in the skin are dilating, you lose water and sweat off salt, and blood pressure drops."

There are other possible factors as well. Cold medicines people take in the winter can raise blood pressure, as can non-steroidal anti-inflammatory painkillers.

Winter Brings Alcohol, Coffee, and Food

Persons also tend to be more depressed in the darker months, leading to more alcohol and coffee consumption, both of which can raise blood pressure, says Dr. Baker.

A more obvious reason: Persons are also often more sedentary in the winter, staying inside and eating more. This can have a secondary effect - weight gain - which also contributes to hypertension.

Dr. Baker believes that these biological or lifestyle differences are more likely to explain the findings than southern or northern climate or the amount of light.

Overall, however, VA hospitals in all the cities studied showed improvements of about 4 percent per year in their ability to keep patients' average blood pressure under control, the study found.

Always consult your physician for more information.

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January 2008

What is Blood Pressure?

Blood pressure, measured with a blood pressure cuff and stethoscope by a nurse or other healthcare provider, is the force of the blood pushing against the artery walls.

Two numbers are recorded when measuring blood pressure. The higher number, or systolic pressure, refers to the pressure inside the artery when the heart contracts and pumps blood through the body.

The lower number, or diastolic pressure, refers to the pressure inside the artery when the heart is at rest and is filling with blood. Both the systolic and diastolic pressures are recorded as "mm Hg" (millimeters of mercury).

High blood pressure, or hypertension, directly increases the risk of coronary heart disease (heart attack) and stroke (brain attack). With high blood pressure, the arteries may have an increased resistance against the flow of blood, causing the heart to pump harder to circulate the blood.

The National Heart, Lung, and Blood Institute (NHLBI) has determined two levels of high blood pressure for adults:

Stage 1
140 mm Hg to 159 mm Hg systolic pressure-higher number
and

90 mm Hg to 99 mm Hg diastolic pressure-lower number

Stage 2
160 mm Hg or higher systolic pressure
and

100 mm Hg or higher diastolic pressure

The NHLBI defines prehypertension as:

120 mm Hg - 139 mm Hg systolic pressure
and

80 mm Hg - 89 mm Hg diastolic pressure

The NHLBI guidelines define normal blood pressure as follows:

Less than 120 mm Hg systolic pressure
and

Less than 80 mm Hg diastolic pressure

Nearly one-third of all Americans have high blood pressure, but it is particularly prevalent in persons with diabetes mellitus, gout, or kidney disease; African Americans (particularly those who live in the southeastern US); persons in their early to middle adult years; persons in their middle to later adult years; women in this age group have higher blood pressure more often than men in this age group (more women have high blood pressure after menopause than men of the same age); middle-aged and elderly people - more than half of all Americans age 60 and older have high blood pressure; persons whose parents or grandparents have/had high blood pressure; obese people; heavy drinkers of alcohol; and women who are taking oral contraceptives.